Ferraroli E, Perulli M, Veredice C, Contaldo I, Quintiliani M, Ricci M, Venezia I, Citrigno L, Qualtieri A, Spadafora P, Cavalcanti F, Battaglia DI. Hereditary Hyperekplexia: A New Family and aSystematic Review of GLRA1 Gene-Related Phenotypes. Pediatr Neurol. 2022 Jul;132:45-49. doi: 10.1016/j.pediatrneurol.2022.05.002. Epub 2022 May 17. PMID: 35636282.
Abstract
Hereditary hyperekplexia (HPX) is a genetic neurodevelopmental disorder recently defined by the triad of (1) neonatal hypertonia, (2) excessive startle reflexes, and (3) generalized stiffness following the startle. Defects in GLRA1 are the most common cause of HPX, inherited both in an autosomal dominant and autosomal recessive manner. GLRA1 mutations can also cause milder phenotypes in the startle syndromes spectrum, but the prevalence is uncertain and no clear genotype-phenotype correlation has emerged yet. Moreover, the prevalence of neurodevelopmental outcomes has not been clearly defined. Here we report a new family of patients with a typical HPX phenotype, linked to a novel GLRA1 mutation, inherited with a recessive pattern. We then perform a systematic review of the literature of GLRA1-related HPX, describing the main epidemiological features of 210 patients. We found that GLRA1-related phenotypes do not necessarily fulfill the current criteria for HPX, including also milder and later-onset phenotypes. Among clinical features of the disease, neurodevelopmental issues were reported in a third of the sample; interestingly, we found that these problems, particularly when severe, were more common in homozygous than in heterozygous patients. Additional clinical and preclinical studies are needed to define predictors of adverse neurodevelopmental outcomes and underlying mechanisms.
Thomas RH, Drew CJ, Wood SE, Hammond CL, Chung SK, Rees MI. Ethnicity can predict GLRA1 genotypes in hyperekplexia. J Neurol Neurosurg Psychiatry. 2015 Mar;86(3):341-3. doi: 10.1136/jnnp-2014-307903. Epub 2014 Jun 26. PMID: 24970905.
Abstract
Objectives: Hyperekplexia is predominantly caused by mutations in the α-1 subunit of the inhibitory glycine receptor (GLRA1). Three quarters of cases show autosomal-recessive inheritance.
Methods: We carefully ascertained reports of ethnicity from our hyperekplexia research cohort. These were compared with all published cases of hyperekplexia with an identified genetic cause. Ethnicities were subgrouped as Caucasian, Asian, Arabic, Turkish, Jewish or Afro-American.
Results: We report the ethnicity of 90 cases: 56 cases from our service augmented by 34 cases from the literature. Homozygous deletions of exons 1 to 7 are predominantly seen in people with Turkish backgrounds (n=16/17, p<0.001). In contrast, the dominant point mutation R271 is seen in people of Asian, Caucasian and African-American heritage (n=19) but not in people with Arab or Turkish ethnicities (p<0.001).
Conclusions: Self-declared ethnicity can predict gene-screening outcomes. Cultural practices influence the inheritance patterns and a Caucasian founder is postulated for R271 mutations.
Chung SK, Vanbellinghen JF, Mullins JG, Robinson A, Hantke J, Hammond CL, Gilbert DF, Freilinger M, Ryan M, Kruer MC, Masri A, Gurses C, Ferrie C, Harvey K, Shiang R, Christodoulou J, Andermann F, Andermann E, Thomas RH, Harvey RJ, Lynch JW, Rees MI. Pathophysiological mechanisms of dominant and recessive GLRA1 mutations in hyperekplexia. J Neurosci. 2010 Jul 14;30(28):9612-20. doi: 10.1523/JNEUROSCI.1763-10.2010. PMID: 20631190; PMCID: PMC6632444.
Abstract
Hyperekplexia is a rare, but potentially fatal, neuromotor disorder characterized by exaggerated startle reflexes and hypertonia in response to sudden, unexpected auditory or tactile stimuli. This disorder is primarily caused by inherited mutations in the genes encoding the glycine receptor (GlyR) alpha1 subunit (GLRA1) and the presynaptic glycine transporter GlyT2 (SLC6A5). In this study, systematic DNA sequencing of GLRA1 in 88 new unrelated human hyperekplexia patients revealed 19 sequence variants in 30 index cases, of which 21 cases were inherited in recessive or compound heterozygote modes. This indicates that recessive hyperekplexia is far more prevalent than previous estimates. From the 19 GLRA1 sequence variants, we have investigated the functional effects of 11 novel and 2 recurrent mutations. The expression levels and functional properties of these hyperekplexia mutants were analyzed using a high-content imaging system and patch-clamp electrophysiology. When expressed in HEK293 cells, either as homomeric alpha1 or heteromeric alpha1beta GlyRs, subcellular localization defects were the major mechanism underlying recessive mutations. However, mutants without trafficking defects typically showed alterations in the glycine sensitivity suggestive of disrupted receptor function. This study also reports the first hyperekplexia mutation associated with a GlyR leak conductance, suggesting tonic channel opening as a new mechanism in neuronal ligand-gated ion channels.
Elmslie FV, Hutchings SM, Spencer V, Curtis A, Covanis T, Gardiner RM, Rees M. Analysis of GLRA1 in hereditary and sporadic hyperekplexia: a novel mutation in a family cosegregating for hyperekplexia and spastic paraparesis. J Med Genet. 1996 May;33(5):435-6. doi: 10.1136/jmg.33.5.435. PMID: 8733061; PMCID: PMC1050620.
Abstract
Hyperekplexia is a rare condition characterised by the presence of neonatal hypertonia and an exaggerated startle response. Mutations have been described in GLRA1, the gene encoding the alpha 1 subunit of the glycine receptor, in dominant families with hyperekplexia and in a single sporadic case, thought to represent an autosomal recessive form of the disease. In this study the coding region of the GLRA1 was analysed in eight probands with hyperekplexia by restriction digest and sequencing. Two familial cases were found to possess the previously described G1192A (R271Q) mutation in exon 6. In an additional family in which hyperekplexia cosegregates with spastic paraparesis, a novel A to G transversion at nucleotide 1206 in exon 6 was detected that changes a lysine at amino acid 276 to a glutamate (K276E). In four sporadic cases no mutations were found. In addition, one familial case did not have a mutation in the coding region of the gene.
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